In the north-easternmost reaches of Navarre, the Alpine ecosystem of Larra is a unique geomorphologic and ecological area. It houses the highest mountains in Navarre and, with a surface area of 120 km2, it is one of the largest karstic areas in Europe, complete with potholes and cavities (S. Martin reaches a depth of 1340 m).

Its highest point: Mesa de los Tres Reyes 2442 m.
And the deepest: The pothole of Contienda (240 m) and that of San Martín, which for years held the world record in terms of depth, at 1340 m.




The massif, formed by cretaceous limestone, is folded, faulted, broken and shaped by water and ice. This gives way to a torturous landscape modelled over millions of years of different climatic cycles, ranging from subtropical to glacial.
Heavy precipitation, often in the form of snow, exceeds 1500 l/m2 a year. The water seeps in through the fissured rock, mining, dissolving and flowing through underground galleries to the Valley of Santa Grazi on the north face.

The surface is covered with open woodland with Spanish pines twisted by the wind, beech trees, service berries and short grass filling hollows. The northern slopes of green grassland on the north face contrast with the proud, naked summits of the Pyrenees. Only rare, specialised flora and fauna thrive in conditions as harsh as these. Rare Alpine flowers, squirrels, dormice, chamois and a good number of birds are the principle inhabitants of this inhospitable place.